Answer: Rakshastal Lake
Notes: Sutlej originates from Rakshastal Lake in Tibet at 4633m elevation. It is Punjab's longest river, enters India via Shipki La in Himachal Pradesh, and is crucial for Bhakra-Nangal Dam, the world's second-largest dam. Catchment area is 56,860 sq km, with a length of 1450 km.
